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<title>io_context::notify_fork</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.io_context.notify_fork"></a><a class="link" href="notify_fork.html" title="io_context::notify_fork">io_context::notify_fork</a>
</h4></div></div></div>
<p>
          <span class="emphasis"><em>Inherited from execution_context.</em></span>
        </p>
<p>
          <a class="indexterm" name="boost_asio.indexterm.io_context.notify_fork"></a> 
Notify
          the <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> of a fork-related
          event.
        </p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">notify_fork</span><span class="special">(</span>
    <span class="identifier">fork_event</span> <span class="identifier">event</span><span class="special">);</span>
</pre>
<p>
          This function is used to inform the <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> that the process
          is about to fork, or has just forked. This allows the <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>, and the services
          it contains, to perform any necessary housekeeping to ensure correct operation
          following a fork.
        </p>
<p>
          This function must not be called while any other <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> function, or
          any function associated with the <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>'s derived class,
          is being called in another thread. It is, however, safe to call this function
          from within a completion handler, provided no other thread is accessing
          the <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> or its derived
          class.
        </p>
<h6>
<a name="boost_asio.reference.io_context.notify_fork.h0"></a>
          <span class="phrase"><a name="boost_asio.reference.io_context.notify_fork.parameters"></a></span><a class="link" href="notify_fork.html#boost_asio.reference.io_context.notify_fork.parameters">Parameters</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">event</span></dt>
<dd><p>
                A fork-related event.
              </p></dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.io_context.notify_fork.h1"></a>
          <span class="phrase"><a name="boost_asio.reference.io_context.notify_fork.exceptions"></a></span><a class="link" href="notify_fork.html#boost_asio.reference.io_context.notify_fork.exceptions">Exceptions</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">boost::system::system_error</span></dt>
<dd><p>
                Thrown on failure. If the notification fails the <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> object
                should no longer be used and should be destroyed.
              </p></dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.io_context.notify_fork.h2"></a>
          <span class="phrase"><a name="boost_asio.reference.io_context.notify_fork.example"></a></span><a class="link" href="notify_fork.html#boost_asio.reference.io_context.notify_fork.example">Example</a>
        </h6>
<p>
          The following code illustrates how to incorporate the <code class="computeroutput"><span class="identifier">notify_fork</span><span class="special">()</span></code> function:
        </p>
<pre class="programlisting"><span class="identifier">my_execution_context</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">(</span><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">fork_prepare</span><span class="special">);</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">fork</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span>
<span class="special">{</span>
  <span class="comment">// This is the child process.</span>
  <span class="identifier">my_execution_context</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">(</span><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">fork_child</span><span class="special">);</span>
<span class="special">}</span>
<span class="keyword">else</span>
<span class="special">{</span>
  <span class="comment">// This is the parent process.</span>
  <span class="identifier">my_execution_context</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">(</span><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">fork_parent</span><span class="special">);</span>
<span class="special">}</span>
</pre>
<h6>
<a name="boost_asio.reference.io_context.notify_fork.h3"></a>
          <span class="phrase"><a name="boost_asio.reference.io_context.notify_fork.remarks"></a></span><a class="link" href="notify_fork.html#boost_asio.reference.io_context.notify_fork.remarks">Remarks</a>
        </h6>
<p>
          For each service object <code class="computeroutput"><span class="identifier">svc</span></code>
          in the <a class="link" href="../execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> set, performs
          <code class="computeroutput"><span class="identifier">svc</span><span class="special">-&gt;</span><span class="identifier">notify_fork</span><span class="special">();</span></code>.
          When processing the fork_prepare event, services are visited in reverse
          order of the beginning of service object lifetime. Otherwise, services
          are visited in order of the beginning of service object lifetime.
        </p>
</div>
<div class="copyright-footer">Copyright © 2003-2025 Christopher M.
      Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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